The present invention relates to a general-purpose grease composition or, more particularly, to a general-purpose grease composition having excellent stability over a wide temperature range.
Needless to say, greases are widely used for the purpose of lubrication, rust-proofing, etc. in a great variety of machines such as freezing machines, traffic vehicles, bearings of rotatable shafts, pumps and many others. Accordingly, the temperature range in which the grease is used remarkably differs depending on the type of the machine. For example, greases used in a freezing machine should exhibit good performance even when the grease is at a very low temperature of -40.degree. to -50.degree. C. as refrigerated by the cooling medium. On the other hand, a grease used in the bearing of a vehicle sometimes encounters an extremely high temperature of 180.degree. to 220.degree. C. when the brake is actuated.
In the prior art, no single grease composition is available which simultaneously satisfies the rather incompatible requirements for the low vaporization loss at high temperatures and adequate torque at very low temperatures as specified in JIS (Japanese Industrial Standard) K 2220 for the greases of Grades 1 to 3 usable in bearings at high and low temperatures. This is mainly due to the properties of the lubricating base oil formulated in the preparation of grease compositions. Therefore, proper selection of the grease has been essential in each machine and for each purpose and troubles are unavoidable when a single grease composition should work satisfactorily in a wide temperature range.